A disc brake is widely used for braking of an automobile. The disc brake includes a caliper in a position to hold a disc rotor that rotates with a wheel. A known caliper used in a disc brake is an opposed-piston caliper including cylinders therein that face opposite side surfaces of the disc rotor, and pistons fitted in the cylinders. In the opposed-piston caliper, two brake pads are placed so as to face inner and outer side surfaces of the disc rotor. In braking of a vehicle, pressure oil is fed into the cylinders to actuate the pistons and thus press the brake pads against the inner and outer side surfaces of the disc rotor, thereby obtaining a braking force.
The caliper used in the disc brake as described above is generally manufactured by casting. In this casting, generally, a so-called core is placed in a metal mold, and a molten aluminum alloy (molten metal) is poured into a cavity that is a space formed between the mold and the core (for example, Patent document 1). The core is a sand mold fitted into a casting mold as a portion for forming a hollow portion in manufacturing a cast (product) having a hollow portion therein. A generally used core is, for example, a shell core manufactured by shell molding of heating and curing silica sand (resin-coated sand) mixed with thermosetting synthetic resin.
The molten metal is poured into the cavity as described above, then, for example, an upper mold (die) and a lower mold (die) that constitute the mold are separated from each other, and the core is removed, thereby obtaining an intermediate product of a caliper. The intermediate product is subjected to various kinds of machining such as cutting or drilling for ensuring accuracy in shape and dimension of each portion, thereby obtaining a caliper.